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Old PSU as benchtop power

Discussion in 'Power Electronics' started by Blue_fog, Mar 1, 2014.

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  1. Blue_fog

    Blue_fog

    17
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    Nov 30, 2011
    Hi,
    I have an old PSU lying around and want to use it for powering my projects. The problem is that the PSU was no longer able to power up my PC. The board's LED would light, but the PC won't turn on. I checked the voltages under no load and they are within +- 10%.

    Is is appropriate to use it to power my projects?I intend to use it for breadboarding(micro controllers) and other stuff.

    Thanks.
    :)
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,473
    2,819
    Jan 21, 2010
    Yeah, that's fine, just remember the following:

    1) The power supply may require a load to operate correctly (although that was only definitely true of older power supplies)
    2) The power supply is capable of producing a lot of power and is not current limited in a practical sense for breadboarding.
    3) the output voltage may be mains ground referenced (so you can't (say) connect two in series to get a higher voltage)

    I have found PC power supplies to be quite tolerant of abuse, and the price is often very right (if you can't get one free you're not trying hard enough :))
     
  3. davenn

    davenn Moderator

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    Sep 5, 2009
    Last edited: Mar 1, 2014
  4. Blue_fog

    Blue_fog

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    Nov 30, 2011
    Should I use a PTC on my breadboard?:confused:
     
  5. Arouse1973

    Arouse1973 Adam

    5,165
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    Dec 18, 2013
    I always thought power good was just a signal telling the PC it is ok to continue, this is the grey wire.

    DC on is the one I thought you grounded and is the green wire.

    Adam
     
  6. davenn

    davenn Moderator

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    yup my mistake now edited

    Dave
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,473
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    Jan 21, 2010
    It's not going to do much good in most cases. It will likely drop the voltage somewhat and be far too slow to react to save a delicate component.

    It's not impossible to add a current limit to a PC power supply, however because the internals are at mains potential and there's not much room to fit stuff, it's not what I would recommend -- especially for a beginner.

    Taking care is better.

    Maybe as a first project you can design something.

    Or you could buy something like this. you can power it from the 12V from the PC power supply and the regulators sound like they are current limited to well under 1A. It doesn't help for higher voltages though.
     
  8. Blue_fog

    Blue_fog

    17
    0
    Nov 30, 2011
    Actually I require some decent amount of current form the supply (I intend to drive a few DC motors). I already have a 12V DC supply capable of outputting 1A but I think that would not be enough for the motors? Also the supply is unregulated and the output is not very smooth. I have used the circuit mentioned here https://www.sparkfun.com/tutorials/57

    Off topic : An intermittent multimeter reading is an indication of noise on the power rail?
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,473
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    Jan 21, 2010
    Fair enough.

    What do you mean by "intermittent multimeter reading"?
     
  10. Blue_fog

    Blue_fog

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    Nov 30, 2011
    The voltage varies between 4.97 to 4.99 volts.
     
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    its varying between xx.97 and xx.99 ... ie its 0.02 of a volt. ?
    that could easily be within the counting accuracy of the meter
    and nothing to do with what is being read

    Dave
     
  12. rickselectricalprojects

    rickselectricalprojects

    118
    12
    Feb 1, 2015
    i use a tattered atx psu i found at the tip for all my projects. i connect all the black wires (but one) and all the yellow wires together and i use that as a high current 12v power supply and i have a single black wire and a single 5v red wire for cirucits and microcontrollers and a single 3.3v orange wire for low voltage projects and i have all those spare 5v and 3.3v wires to put together if i ever need high current 5v or 3.3v:)
    so yes in my opinion a computer psu makes an excellent benchtop psu.
     
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